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Thread: Using source stream in transcoder ngrp

  1. #1
    Join Date
    Aug 2013

    Default Using source stream in transcoder ngrp

    I have done some brief experimenting with using the source stream as part of the transcoder streaming group so that I don't have to waste CPU running the source resolution/quality feed through the transcoder just to get the same thing out the other end. Unfortunately, when the adaptive stream switches to the highest quality, it jumps a few seconds, and same with when it goes from the highest quality (source) to one of the transcoded feeds.

    Has anyone gotten source to work successfully as a member of a transcode group? Or do we have to waste the CPU cycles to generate a transcoded stream with the same resolution and bitrate as our source in order to offer the highest quality to our viewers?

  2. #2
    Join Date
    Jul 2012


    There is going to be some minor time difference between source and the transcoded streams. This is due to the processing time required to generate the transcoded streams. The variance will differ between systems with more or less CPU/GPU capabilities.

    That said, running with the _source encode block enabled, and using PassThru settings for the audio and video codec container, will not require as much CPU as you may think. Other, more aggressive transcoder streams are set to reduce bit rate, change codecs, modify key frames, stretch/crop, add overlay, etc. will consume dramatically more CPU resources.

    As a test, turn off all your transcodes and leave only the _source set to true with PassThru set for video and audio. Monitoring your server performance, you will see that it uses very little CPU to process a PassThru stream. In fact, it uses about the same CPU as an application that does not have the Transcoder enabled.

    I would suggest that you include the _source stream in your encode blocks to maintain the closest synchronization with all over your ABR streams.



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